The present invention relates to scanning an object with an external electric field, in which at least one transmission line is energised by the application of an input voltage. The present invention also relates to an apparatus for scanning an object.
It is known to provide a sensor that includes a dielectric layer that presents a surface defining the base of a volume in which a test object may be placed in order to sense the electrical permittivity of an object, as described in U.S. Pat. No. 8,994,383 assigned to the present applicant. Signals are applied to a first electrode to produce an electric field that extends outside the sensor. An output signal is then produced in a second electrode by capacitive coupling, from which the electrical permittivity of the volume may be deduced.
In a security environment, dangerous items contained within packages or even items of clothing, such as shoes, may be detected from measurements of permittivity. A dangerous material could be included in the heel of a shoe for example. However, given that shoes come in many shapes and sizes, problems arise in terms of ensuring that the generated electric field penetrates sufficiently into an area of interest.